Residential automatic fire protection sprinklers are typically designed to specific performance criteria or standard that has been accepted by industry. The performance criteria establishes the minimum performance standards for a given sprinkler to be consider sufficient for use as a residential fire protection product. For example, Underwriters Laboratories Inc. (UL) “Standard for Safety for Residential Sprinklers for Fire Protection Service” (October 2003) (hereinafter “UL 1626”), which is incorporated herein in its entirety be reference thereto, is believed to be an accepted industry standard.
The National Fire Protection Association (NFPA) also promulgates standards relating to residential fire protection such as, for example, (i) NFPA Standard 13 (2002) (hereinafter “NFPA 13”); (ii) NFPA Standard 13D (2002) (hereinafter “NFPA 13D); and (iii) NFPA Standard 13R (2002) (hereinafter “NFPA 13R”) (collectively “NFPA Standards”) each of which is incorporated in its entirety herein by reference thereto. In order for a residential sprinkler to be approved for installation under NFPA Standards, such sprinkler typically must pass various tests, for example, tests promulgated by UL under UL 1626, in order to be listed for use as a residential sprinkler. Specifically, UL 1626 generally requires a sprinkler, as described in Table 6.1 of Section 6, to deliver a minimum flow rate (gallons per minute or “gpm”) for a specified coverage area (square feet or “ft2”) so as to provide for a desired average density of at least 0.05 gpm/ft2. For instance, for a 16 ft.×16 ft. room size with a 256 ft2 coverage area, a residential sprinkler that can provide the minimum density in an optimum manner would utilize a flow of water of thirteen gallons per minute (13 gpm). Thus, 13 gpm is the minimum flow listing for a coverage area of 256 ft2. In addition to a sprinkler configuration providing the minimum density at the minimum flow listing, the sprinkler advantageously would achieve the minimum flow listing at the lowest possible pressure. The minimum flow rate tabulated in Table 6.1 can be used to calculate a predicted minimum fluid pressure needed to operate a sprinkler by virtue of a rated K-factor of the sprinkler. A rated K-factor of a sprinkler provides a coefficient of discharge of the flow passage of the sprinkler, is defined as follow:
      K    -    factor    =      Q          p      
where Q is the flow rate in GPM and p is the pressure in pounds per square inch gauge. Thus, for a rated K-factor of 4.9 and a minimum flow rate of 13 gpm, the residual or calculated minimum pressure is seven pounds per square inch (7 psi.).
In order for a sprinkler to pass actual fluid distribution tests as described in Sections 26 and 27 of UL 1626 however, the actual minimum pressure of the test sprinkler may differ from the calculated or predicted minimum pressure, which can be calculated using the given minimum flow rate of Table 6.1 in UL 1626 and the rated K-factor of the sprinkler. Further, the actual minimum fluid flow rate to pass these distribution tests of UL 1626 for a specified coverage area may even be higher than the tabulated minimum flow rate given in Table 6.1 of UL 1626. Consequently, any attempt to provide for a listed sprinkler (i.e., an operational sprinkler suitable for the protection of a dwelling unit) cannot be predicted by applications of a known formula to known residential sprinklers.
In order to provide an aesthetically appealing configuration of a sprinkler for use in a residence, the sprinkler may be configured to use a flat plate to conceal the sprinkler itself until the sprinkler is actuated. This type of sprinkler is known as a residential flat plate concealed sprinklers. It is believed that known residential flat plate concealed sprinklers that are configured for use in a pendent manner range in K-factor from 4.1 to 5.6 (gpm/psi1/2).
In order for a residential flat plate concealed sprinkler to operate, a two step operation occurs when a fire hazard is to be addressed. First, the cover of the concealed sprinkler must disengage from the sprinkler. Second, the sprinkler must operate to allow water to flow. Because of the two step operation of the residential flat plate concealed sprinkler, and that such residential sprinklers are typically fully recessed into a ceiling, residential flat plate concealed sprinklers have an increased flow rate above the minimum flow listings in order to successfully pass UL 1626 fire tests.
It is believe that known residential flat plate concealed sprinklers have been unable to successfully pass the UL 1626 test standard for a 16 ft.×16 ft. room size fire test at both the minimum flow rate (13 gpm) and the minimum operating pressure (7 psi). Furthermore, it is also believed that known residential flat plate concealed sprinklers have been unable to successfully achieve the minimum flow rates of seventeen gallons per minute (17 gpm.) for an 18 ft.×18 ft. room size and twenty gallons per minute for a 20 ft.×20 ft. room size in accordance with UL 1626.